The long-term goal of this project is to understand the mechanisms of eosinophilic inflammation in human diseases. There are fundamental questions and controversies that need to be addressed. What initiates the Th2-like immune response in eosinophil-associated disorders, such as asthma? What roles do eosinophils have in the phenotypes of these diseases? Eosinophilic airway inflammation can be provoked in non-sensitized animals after brief exposure to an environmental organism implicated in human asthma, Alternaria;furthermore, eosinophils degranulate after in vitro exposure to Alternaria. Bioactive enzymes released by Alternaria could provide an innate cue towards the Th2 response and eosinophil activation. The overall hypothesis is as follows: innate immune responses provoked by immunoactive enzymes derived from environmental fungi, such as Alternaria, activate conventional NK cells and eosinophils in the airways, induce their production of Th2-like cytokines and pro-inflammatory mediators, and promote the airway pathologic changes observed in human asthma. Aim 1 proposes to investigate the role of NK cells in initiating the eosinophilic airway inflammation in response to Alternaria and to characterize the NK cell receptors involved in their responses to this fungus. Aim 2 proposes to collaborate with an Alternaria functional genomics expert and to identify and characterize the fungal proteases and glycolytic enzymes, which are involved in the innate responses to Alternaria by NK cells and eosinophils. Aim 3 proposes to investigate the role(s) of eosinophils, which have been activated by Alternaria and its enzymes, as potent pro-inflammatory effectors in the airway pathology of asthma. Unlike the role of the Toll-like receptor-mediated innate response to "pathogen-related molecular patterns" in the development of Th1 immunity, little is known about the innate arm of Th2 immunity. Achieving the goals of this project will produce a new and better understanding of the immunological and pathological mechanisms of human asthma and eosinophilic inflammation and identify key innate molecules driving the airway Th2 response. Relevance: Patients with asthma have persistent respiratory problems. This research will investigate how the interaction of immune cells and our environment cause and worsen the disease.